Imagine your name is James but you prefer to go by Jim. Technically, Jim is not your name. If you tell somebody you prefer to be called Jim and they keep calling you James, are they not being an asshole?
Imagine you have a dick, but feel like a lady and wish to be addressed as Miss instead of Sir. Technically, your sex is not female. But if somebody insists on calling you sir after being informed of your preference, are they not being an asshole?
There is a person who sometimes comes into my dad's place of work dressed like a man and, more or less, acts like a man. Other times, he comes in dressed as a woman and acts like a woman. One day, my dad asked this person - who was dressed as a man - "are you a guy or a girl today?" My dad was clearly being a dickhead.